Искра 122 калькулятор ремонта

ЭВМ и ПЭВМ, производившиеся в СССР и странах СЭВ
system11
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Искра 122 калькулятор ремонта

Сообщение system11 » 29.01.2021,01:12

Hi, firstly apologies for writing in English, I will follow with a Russian machine translation but I can't speak Russian - sorry!

I have a couple of Iskra 122 calculators, one had a fault and by swapping PCB boards between two machines I was able to isolate the fault to board 7102622. This PCB has K172TP1, K172ЛM1, K172ЛИ1, K172ЛK1 chips, is there any way to test these chips for obvious faults? I am used to normal 5v TTL logic chips but I have no experience of these at all and my only solution would be to replace all of the parts one by one. If there is a better solution, help would be appreciated.

thanks!

Привет, во-первых, извиняюсь за то, что написал на английском, я сделаю русский машинный перевод, но я не говорю по-русски - извините!

У меня есть пара калькуляторов Искра 122, у одного была неисправность, и, поменяв местами платы печатных плат между двумя машинами, я смог изолировать неисправность на плате 7102622. На этой плате есть микросхемы К172ТР1, К172ЛМ1, К172ЛИ1, К172ЛК1, есть ли способ проверить эти фишки по явным неисправностям? Я привык к обычным 5-вольтовым логическим микросхемам TTL, но у меня нет опыта с ними вообще, и моим единственным решением было бы заменить все части одну за другой. Если есть лучшее решение, мы будем благодарны за помощь.

благодаря!
iskra_7102622.jpg

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Искра 122 калькулятор ремонта

Сообщение DonkeyHot » 29.01.2021,07:59

172 series has -27V power supply,
Here is the datasheet for 172LK1
https://eandc.ru/pdf/mikroskhema/k172lk1.pdf
ZX/XT Самоделкин
Продам <- обновляю без апа, заходите.

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Искра 122 калькулятор ремонта

Сообщение Sergei Frolov » 29.01.2021,09:51

On the K172 series, ICs shound have strong 0V and can be little float -12V. If you have voltages between -1 and -10V on the outputs, this is strange.
Many of K172 ICs has complimentary outputs (normal and inverted), so you may check both outputs.
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Искра 122 калькулятор ремонта

Сообщение system11 » 29.01.2021,16:26

I have an oscilloscope I can use to check the outputs, but I will need to order an adjustable power supply so I can apply power to the chips, it seems like checking with the PCB installed will be very difficult due to limited space for access. I've identified the voltage pins on the edge connector so can supply power there, so it seems like this should work:

PSU PCB
+27v -> 0v
0v -> -27V

The ground reference for the oscilloscope probe should be connected to 0v on the PCB (in reality, +27V from PSU). Not ideal checking them out of circuit this way but I'm trying to reduce any risk to the calculator.

Interesting that the whole PCB seems to be dipped in clear coating, even the chip legs and cases are coated. I've never seen this before but it seems to have provided good protection for the labels and legs from fading or corrosion.

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Искра 122 калькулятор ремонта

Сообщение Sergei Frolov » 29.01.2021,16:34

On some calculator models you may connect oscilloscope GND to the calculator's shassic.
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Искра 122 калькулятор ремонта

Сообщение Кай » 29.01.2021,16:46

the whole PCB seems to be dipped in clear coating, even the chip legs and cases are coated. I've never seen this before
This is the standard varnish for produced to industrial and military PCB in the USSR and Russia. Urethane two-component thermo- and chemical- resistant varnish UR-231. At primitive - epoxy glue.

http://www.155la3.ru/k172.htm MB link contain some help 2U.

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Искра 122 калькулятор ремонта

Сообщение system11 » 29.01.2021,18:56

Thanks, I will see if I can find some UR-231 or similar so after repair it will be back to 'factory condition'.

I think I've found a chip to look at first - I was checking to see if any of the outputs on these chips were shorted to -27V or 0V internally which would be a definite fault, and one of them is on a K172TP1 pin 9. However, under the chip the original factory soldering is the cause of the short, it's a very small solder bridge and hard to see, I compared to my others and this is not correct.

It would not affect operation when new as this output is not connected to anything except pin 8, but perhaps it could have caused stress and early failure. I have seen similar with some TTL chips if someone ties a data line high or low directly without using resistors.

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Искра 122 калькулятор ремонта

Сообщение Кай » 29.01.2021,20:06

chip to look at first
Be oversure to check K172ЛИ1. This is the least reliable IC's from that series. Produced "at an edge/kneeve".

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Сообщение Sergei Frolov » 30.01.2021,16:33

It is best to repair with a transit board. You may also tear off the PCBs and check the logic levels from the bottom of the calculator.

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Искра 122 калькулятор ремонта

Сообщение system11 » 31.01.2021,01:15

I think I can make something like that, I work on arcade games mostly and one of the common connector extensions could be cut in half, they are 2x28 pin but with no split in the middle, same pitch.

I managed to find the negative calculation fault on my other 122, it is caused by the first of the 5 middle boards in the PCB rack (7102618) - again a lucky test picking it first time. So now I have two fully working model 122 using donor boards. One is very clean and original, one is cosmetically very poor. The donor is cosmetically good but the keyboard frame and keys are bent from something heavy being stored on top probably. I took all the parts off today to be straightened and cleaned. Hopefully I can repair all three machines, but if not I can certainly make two good ones now. The PCB retainer bracket is missing from one of them, and the metal plate with the decimal position controls printed on it.

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Искра 122 калькулятор ремонта

Сообщение Zerthimon » 03.02.2021,12:32

system11 писал(а): 29.01.2021,01:12 is there any way to test these chips for obvious faults?
There is a chip tester from Trolsoft ( https://trolsoft.ru/en/chip-tester ) that is able to test some of the chips produced in the USSR. Probably not the 172 series chips though :(
del

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